1. Field of the Invention
The present invention relates to a webbing retractor for use in a seatbelt system designed to protect an occupant of a vehicle when an emergency situation occurs, the apparatus being employed to wind up an occupant restraining webbing from one end of the same which is retained thereby.
2. Description of the Prior Art
A conventional webbing retractor which is employed in a seatbelt system and is adapted to wind up an occupant restraining webbing from one end thereof includes a webbing takeup shaft which is disposed therein and retains one end of an occupant restraining webbing.
FIG. 8 is an exploded perspective view of a webbing takeup shaft generally employed. The takeup shaft includes a winding drum 10 which is formed by bending a metal plate material into a cylindrical shape. The winding drum 10 has engagement projections 10A formed at both axial ends thereof. The engagement projections 10A are respectively received through engagement bores 14 which are formed in ratchet wheels 12, and the respective distal end portions of the projections 10A are caulked, whereby the winding drum 10 and the ratchet wheels 12 are assembled into an integral structure. A looped portion 18 which is formed at one end of an occupant restraining webbing 16 is inserted into the inside of the winding drum 10 through a notch 20 formed in a portion of the winding drum 10. A pin 22 which is inserted into the central axis portion of the winding drum 10 is fitted into the looped portion 18 in such a manner as to expand the diameter of the looped portion 18, whereby the looped portion 18 is prevented from being pulled out from the winding drum 10. Thus, one end of the webbing 16 is retained by the winding drum 10.
Such a conventional takeup shaft structure, however, suffers from the following disadvantages. Namely, if the winding drum 10 is formed from a thin metal plate, it may be deformed and lead to an increase in the length of the webbing 16 which is undesirably wound off at the time of occurrence of a vehicular emergency situation. Further, when the diameter of the winding drum 10 is increased for the purpose of increasing the winding force thereof or of reducing variations in the winding torque, the weight of the takeup shaft as a whole is undesirably increased since the winding drum 10 is made of a metal.